Alloys for improving properties of graphite



UN 391-309493 UK United States Patent M 3,436,253 ALLOYS FOR IMPROVING PROPERTIES OF GRAPHITE Royal W. Kelsey, Santa Clara, and Donald D. Crooks, and Henry T. Sumsion, San Jose, Calif., assignors, by mesne assignments, to the United States of America as represented by the Secretary of the Navy No Drawing. Original application Nov. 27, 1963, Ser. No. 326,643. Divided and this application Apr. 13, 1966, Ser. No. 566,452

Int. Cl. F02c 7/30; B32b /16; C22c 25/00 US. Cl. 117-160 1 Claim This application is a division of copending US. application Ser. No. 326,643, filed Nov. 27, 1963, by present applicants.

This invention relates to alloys and more particularly to alloys which will wet, coat and impregnate graphite.

For a number of years there has been a continuing search for inert materials capable of withstanding the high temperatures experienced in jet and rocket engines and nozzles. Graphite has been found to possess many necessary and desirable properties when used for these purposes. There is, however, constant effort to improve the mechanical and chemical properties of graphite in order to satisfy the demands for higher strengths and greater resistance to corrosion and erosion.

Therefore, objects and features of the present invention include the provision of material which when applied to the surface of graphite will inhibit corrosion and erosion.

Another object of the present invention is to provide a surface treatment for graphite articles which will materially increase the strength of the graphite.

A further object of the present invention is to provide a protective surface coating for graphite objects for use in corrosive environments at elevated temperatures.

Another object of the present invention is the provision of a material for coating and impregnating graphite which will increase the strength and prolong the service life of graphite articles subjected to a corrosive environment and erosive influences at elevated temperatures.

Another object of the present invention to is provide an economical coating process for graphite articles which will greatly increase the strength and resistance to corrosion and erosion of the article.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description.

Alloys which satisfy the objects of the present invention comprise essentially titanium-rich and zirconium-rich beryllium mixtures which upon melting will wet, coat and impregnate graphite.

Numerous methods may be utilized for purposes of providing graphite articles with the surface coating of the instant invention. For example, one process of wetting, coating and impregnating a member of graphite comprises melting one of the selected alloys on the graphite member to be impregnated in a vacuum or inert atmosphere at normal or reduced pressure, Another suitable coating process comprises dipping the graphite piece to be impregnated into a molten pool of any of the subject alloys. Reaction of the alloy constituents with the graphite is limited at the relatively low temperatures and times involved and a minimum of carbide is formed. If desired, however, complete carburization can be accomplished as may be required for some applications of this invention. Other coating methods which are standard practice in the art of coating and which may become apparent to those skilled in the art could be used and such are not intended to be included within. the scope of this invention.

3,436,253 Patented Apr. 1, 1969 Particularly advantageous graphite coating alloys for use in high temperature corrosive environments are titanium base alloys in the range of about 1 to 20 weight per cent beryllium. Within this range alloys near the eutectic, that is, a composition near 5 weight percent beryllium balance titanium, are considered to be most desirable and advantageous. Alloys near the eutectic in this system have been shown to have the lowest melting point, the highest fluidity and the greatest impregnation capabilities without excessive temperature and consequent gross carbide formation. The melting range for the 5 weight percent beryllium balance titanium alloy is approximately 1000 to 1150 C., a temperature well below the melting points of beryllium (1285 C.) and titanium (1800 C.). Tests to determine the limits of suitability of titanium base alloys having more than 20 weight percent beryllium for graphite coating have been inconclusive.

Zirconium-beryllium alloys within the range of about 1 to 20 weight percent beryllium balance zirconium have also been found to be suitable for wetting, coating and impregnating graphite articles. The zirconium-beryllium alloys, however, have been found to possess higher melting points than the titanium-beryllium mixtures. For this reason, the zirconium-beryllium alloys are particularly suitable and adapted for graphite coating wherein canburization is not a detriment.

This invention is significant in that graphite, which is admirably suited for structural, high temperature uses, may now be used for rocket nose cones, motor cases and the like. This utility is achieved by virtue of an in-= crease in strength and resistance to air corrosion and erosion due to the application thereon of the protective coating disclosed herein. It is thus apparent that the objects of the present invention have been accomplished in an economical corrosion and erosion retarding, graphite strengthening alloy coating for graphite articles particu-= larly for use in environments of elevated temperature and corrosive influences.

What is claimed is:

1. A composite article for use under conditions of elevated temperatures comprising a substrate of graphite coated and impregnated with a layer of alloy material having a composition of from about one to twenty weight percent beryllium, balance being a material selected from the group consisting of Zirconium and titanium said article being characterized by an increase in strength and resistance to air corrosion and erosion.

References Cited UNITED STATES PATENTS 2,929,741 3/1960 Steinberg 117-119 X 3,007,824 11/1961 McQuillan et al. -175.5 X 3,093,514 6/1963 McCallum et al. 75-175.5 X 3,288,573 11/1966 Abos 117-160 X 3,366,464 1/1968 Guichet et al. 117-160 X OTHER REFERENCES Hansen: Constitution of Binary Alloys, McGraw-Hill (1958), p. 298.

Larsen: Some Preliminary Data on Alloys of Titanium, Titanium Symposium, paper No. 12, Dept. of Navy, ONR, Washington, DC, Dec. 16, 1948, p. 3.

RALPH S. KENDALL, Primary Examiner.

US. Cl. X.R. 

1. A COMPOSITE ARTICLE FOR USE UNDER CONDITIONS OF ELEVATED TEMPERATURES COMPRISING A SUBSTRATE OF GRAPHITE COATED AND IMPREGNATED WITH A LAYER OF ALLOY MATERIAL HAVING A COMPOSITION OF FROM ABOUT ONE TO TWENTY WEIGHT PERCENT BERYLLIUM, BALANCE BEING A MATERIAL SELECTED FROM THE GROUP CONSISTING OF ZIRCONIUM AND TITANIUM SAID ARTICLE BEING CHARACTERIZED BY AN INCREASE IN STRENGTH AND RESISTANCE TO AIR CORROSION AND EROSION. 